Abstract
Non-random mating plays a key role in speciation and impacts the individual life history. Body size is one of the most important traits by which the mate choice is carried out. Various patterns of body size preference are known in fi sh, but this component of reproductive strategy has been studied in a limited number of species. Although the climbing perch (Anabas testudineus) is widespread and well-known, few descriptions of its spawning have been published, only in captivity and in most cases artifi cially induced with hormonal agents. This paper describes the main features of natural spawning of the climbing perch in aquarium compared to induced spawning. A positive size-assortative mating has been revealed. The mating system of these fish has been shown to be fl exible, presumably ranging from monogamy to polygamy. The results are discussed in the context of the general issue of the adequacy of fi sh behaviour research methods.